Preference shares

Dear Mr Tan, 
I used to buy Singapore Government Bonds, when yields were at 2 to 3%. Now it is not worth my trouble. 

I am aware of preference shares that are issued by DBS, UOB and OCBC.  For OCBC, their coupons are 3.93%, 4.2%, 4.5% and 5.1%. This is what I am most familiar with. I bought a small amount for my mum's retirement fund. 

In summary, they are perpetual and non-cumulative. Of course the other risks associated with debt securities apply. 
They are rather illiquid. Looking at the OCBC annual report, one can see that they are held in rather large quantities by institutions. 

I read in Benjamin Graham's The Intelligent Investor that the best time to buy them is during market turmoil when prices are depressed. That is when the yields are sufficiently high to compensate for the potential risks. 

NL